First you need to create a "company" profile for your firm. If you don't have one already:
In the header of your profile, click "Edit" to reveal a control to set your company type. Enter "Incubator", "VC Firm", or whatever label is appropriate. You're all set.
After you have created a company profile and set the Company Type to "Accelerator", visit the "Applications" profile tab and click [Add an Application].